1. Field of the Invention
The Present invention generally relates to a substrate processing method or apparatus for supplying etching liquid toward a top or reverse face of a rotating substrate to carry out etching processing. Examples of substrates to be processed include semiconductor wafers, glass substrates for liquid crystal displays, glass substrates for plasma displays, substrates for FEDs (field emission displays), substrates for optical discs, substrates for magnet discs, substrates for magnet-optical discs, glass substrates for photomasks, substrates for ceramics, substrates for solar cells, or the like.
2. Description of Related Art
The substrate processing apparatus described in Japanese Unexamined Patent Application Publication No. 2002-336761 comprises a spin chuck for horizontally holding and rotating a wafer and a liquid supply nozzle for supplying a processing liquid toward the wafer held by the spin chuck.
The liquid supply nozzle is held by a holding member. The holding unit is supported by a rotational pivot connected to a rotation axis of positive/negative rotational motor. Also, liquid supply nozzle connects to a liquid supply pipe, which liquid supply pipe connects to an etching liquid supply pipe connected to an etching liquid supply member. Etching liquid is supplied to the liquid supply nozzle. Etching liquid spouted from the liquid supply nozzle is supplied toward the substrate in a state where the substrate is rotated by the spin chuck.
Specifically, the positive/negative rotational motor rotationally moves the liquid supply nozzle over the substrate, in a state that the liquid supply nozzle discharged an etching liquid, so that the etching liquid application position on the top face of the substrate shifts toward the center portion of the substrate (scan step). Thereafter, when the etching liquid application position reaches the center portion of the substrate, the positive/negative rotational motor stops the rotational movement of the liquid supply nozzle. After the rotational movement of the liquid supply nozzle is stopped, spouting of the etching liquid from the supply liquid nozzle toward the center portion of the substrate is continued for a predetermined time (CENTER SPOUT STEP). After the etching liquid from the liquid supply nozzle is stopped, The positive/negative rotational motor moves the liquid supply nozzle out of the area above the substrate by reversibly rotating a rotational shaft thereof.
In a substrate processing apparatus described in Japanese Patent Application Publication No. 2002-336761, etching processing is carried out taking into consideration of the difference of etching amounts between the edge portion and center portion in the center discharge step and differences of etching amounts between the edge, portion and center portion in the scan step.
More specifically, the temperature of the etching liquid supplied toward the principal face of the substrate in the center discharge step decreases toward the edge portion of the principal face of the substrate affected by vaporization heat. Accordingly, the center portion of the principal face of the substrate is etched deeper than the edge portion thereof, thereby increasing the amount of etching in a concentric manner from the edge portion toward the center portion. On the contrary, in the scan step, the edge portion of the principal face of the substrate is etched deeper than the center portion thereof because the former is exposed to the etching liquid longer than the latter, thereby increasing the amount of etching in a concentric manner from the center portion toward the edge portion.
The substrate processing apparatus described in Japanese Unexamined Patent Application Publication No. 2002-336761 carries out the scan step and center discharge step in order to offset the difference of etching amount between the edge portion and center portion of the principal face of a substrate, thereby it is possible to increase uniformity than in a case that only a center discharge step is carried out.
However, it must be noted that changes of supply condition of an etching liquid (center discharge condition) result in changes of etching conditions (distribution of etching amount). Thus changes of a center discharging condition may result in a decrease of etching uniformity at the final stage, unless changes are made as to supply conditions of etching liquid in the scan step such as scan rate and the like in concert with the changes of the center discharging condition. Due to lack of measures taken for such matters, the substrate processing apparatus described in Japanese Unexamined Patent Application Publication No. 2002-336761 may yield a low uniformity for certain etching conditions.
Also, with sophistication of devices formed on substrates, there is a growing demand for higher level of uniformity in etching. While amounts of etching are varied, uniform etching is required for each amount of etching.
Japanese Unexamined Patent Application Publication No. H11-307492 discloses a method of varying scan velocity according to a given equation (V1=V0/R). Likewise, U.S. Patent Application Publication No. 2012/318304 A1 discloses a method of varying scan velocity according to a given equation V(r) XRa=constant.
It is conventionally known that etching amount in an edge portion of a substrate is lower than that in a center portion of the substrate, degrading uniformity of etching. By adapting the methods described in the Japanese Unexamined Patent Application Publication No. H11-307492 or U.S. Patent Application Publication No. 2012/318304 A1, it may be possible to achieve lesser degradation of etching uniformity due to lower etching amounts in an edge portion of a substrate.
However, it is not possible to offset the difference between etching amount in a center portion of a substrate and etching amount in an edge portion of the substrate according to a single equation in an across-the-board manner. Also, etching behaviors in edge portion of a substrate differ for every etching condition. Therefore, in practice, it is needed to find, through experiments, conditions with which degradation of etching amount in an edge portion of a substrate can be suppressed.
Unlike the present invention, neither the method described in the Japanese Unexamined Patent Application Publication No. H11-307492 nor the method described in the U.S. Patent Application Publication No. 2012/318304 A1 does not address to such problems.
Further, with these methods, scan velocity is changed in a continuous manner. More complicated control is needed for changing of scan velocity in a continuous manner than that in a stepwise manner. Thus it is preferable to change scan velocity in a constant or stepwise manner.